The present invention relates to a method and arrangement for practising the method for the optimal supplying of autotrophic organisms with carbon dioxide nutrient, the nutrient requirement fluctuating in dependence on growth and thus on the incident light, temperature and the density of the organisms.
In all cultures of photoautotropic organisms, carbon dioxide must be supplied as the main nutrient. The carbon dioxide attaches itself to water and forms carbonic acid which then dissociates into hydrated H.sup.+ ions and HCO.sub.3.sup.- ions. Every introduction of CO.sub.2 into aqueous systems in the slightly acid to alkali range, as, for example, nutrient solutions for algae, is thus connected with a reduction in pH. Conversely, every removal of CO.sub.2 or H.sub.2 CO.sub.3, respectively, or of HCO.sub.3.sup.- leads to a rise in pH. The quantity of CO.sub.2 required by the organisms at a certain point in time depends on a plurality of factors, mainly, light, temperature and density of the organisms. Under certain circumstances, in particular, under controlled out door conditions, the quantity of CO.sub.2 required by the organisms is subject to considerable fluctuations.
There have been attempts to provide economically justifiable quantitites of CO.sub.2 supplies which are always the most favorable under fluctuating conditions, but this has not been possible with conventional systems for introducing CO.sub.2 into the cultures. These known systems are described, for example, in the summary report by the German Botanical Society, Volume 83, Issue No. 11 (1970), pages 589 to 606, and introduce the CO.sub.2, which is important for the growth of the microorganisms, e.g., the algae, either intermittently by means of diffusion boxes or constantly and uniformly through bypass gas exchangers. The former system using intermittent CO.sub.2 introduction, according to 1), has the advantage of good CO.sub.2 utilization, but has the drawback that it requires much work to fill the system with CO.sub.2, the upwardly closed diffusion boxes are difficult to clean, flow resistance is high and the yields per unit area or algae growth, respectively, are relatively poor due to insufficient CO.sub.2 supply. On the other hand, any type of system using constant and uniform CO.sub.2 introduction has the drawback that it will not be optimally adapted to the prevailing light conditions which principally fluctuate in the course of a day, so that over long periods of time there will exist a lack of CO.sub.2 or an excess of CO.sub.2. FNT 1) H. Kraut and M. -E. Meffert, Forschungsber. Land Nordrhein-Westfalen, No. 1648, p. 12-13 (1966)